What are possible functions assigned on decision nodes for decision tree prediction?
For a binary split, there are only three possible operations (or arguably only two if you consider one-hot encoding). Any other kind of split would simply not be binary. Almost every tree-based model is restricted to binary splits, due to the combinatorial explosion when considering ternary or even more complex splits.

Of course you could write your own algorithm that uses recursive non-binary splits. Beware though that you'll be facing the same difficulty that has led the vast majority of algorithms to be limited to strictly binary splits.

Have a look at this related question.